O'Brien must suffer! Keiko gets possessed by an evil pah-wraith, and Rosalind Chao finally gets to stretch her acting muscles and does a damn good job. I always enjoyed this episode, partly for that above reason and partly because the whole thing is fun and really well paced. In fact everyone here gets to do some really good work, from Colm Meaney as the heavily-under-pressure Chief, to Rom and his new life as station engineer.
This is funny, exciting and unexpected. Bashir and O'Brien get some great stuff together, and even little Molly gets in on it. A lot of people seem to hate the pah-wraiths, mostly because they were a bit of a lazy concept, but I don't really have that problem and I always was a fan of the Bajoran religious system that evolved through the show.
Keiko seemed nicer than usual, for some reason, in this episode :D
I was never a huge fan of the alien-mind-takes-over-body episodes. They did to many of those overall. I know they wanted to introduce the Pah´wraith, it would have been nice if they had found another avenue.